mx.dnsassurance.com has no NS records.
NS records for this zone are defined at dnsassurance.com.
NS records for this zone are defined at dnsassurance.com.
Question and response
Question
dig mx.dnsassurance.com. NS
Answer
The response has no answer records.
Authority
dnsassurance.com. 86400 SOA av4.nstld.com. nstld.verisign-grs.com. 1772842709 1800 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0